Currently, there are over 2 million hospitalizations and nearly 10 million visits to physicians that are associated with coronary heart disease in the United States every year. A majority of these patients receive some form of antiplatelet therapy, e.g. Aspirin, Plavix, etc., to prevent acute thrombosis and clotting associated with vascular interventions, such as angioplasty, or implants, such as coronary stents. Excess dosage of the antiplatelet drugs can result in bleeding complications because the platelet function is over-suppressed, while insufficient dosage can fail to prevent acute thrombosis and clotting due to insufficient suppression of platelet function. Thus, it would be valuable to assess platelet function in patients at certain points of care and adjust the antiplatelet drug dosage to the specific needs of each individual. The relevance of such a point-of-care approach is becoming increasingly important in the context of platelet GP IIb/IIIa antagonists, e.g. Abciximab, Tirofiban, Eptifibatide, etc., with short half-lives (typically about 1 hour) that can be adjusted carefully and quickly to meet the needs of each patient. Thus, an effective point-of-care platelet function assay that enables management of therapeutic regimen has considerable clinical value.
A platelet aggregometer is an instrument that can assess certain aspects of platelet function. This device can be used by starting with a platelet suspension, such as blood or platelet rich plasma, which can be collected from a patient and dispensed into a disposable sample holder of the platelet aggregometer. A chemical stimulus, such as collagen, can be added to the platelet suspension in the sample holder, and subsequent agitation/mixing of the platelet suspension with the stimulus can cause the platelets to aggregate. The characteristics of this aggregation can be measured by various methods known by those skilled in the art, and the degree of aggregation measured can be directly related to the function of the platelets.
Currently available methods in the field of platelet aggregometers include sample holders that provide thorough mixing and agitation of the platelet suspension to cause platelet aggregation. However, most of these methods and devices create flow that is not conducive to enabling certain detection modalities of platelet aggregation, particularly for light scattering methods.
Many methods utilize mechanical mixing which often damages or otherwise alters fluid characteristics. For example, the use of a roller pump has been one proposed method for moving blood. However, the compression of a flow conduit containing blood by means of rollers often disfigures platelet aggregates, damages red cells, and alter their characteristics. Thus, the ergonomics of such designs can be undesirable, and loading of the blood sample and/or the chemical stimulus that causes platelet aggregation can be cumbersome. These limitations detrimentally influence the quality and consistency of platelet aggregation, which in turn adversely affects the reproducibility and reliability of the measurement of platelet function. Other methods include designs that present relatively good flow patterns for measurement using light scattering techniques, but do not provide significant mixing that induces more thorough and consistent platelet aggregation.